The transect of La Plata Valley (Map 65) is between the crater
of the volcano Puracé and the Serranía de las Minas, which is north of the Upper
Magdalena River Valley - where the Central and Eastern cordilleras diverge northward from
the Colombian Central Massif (Gran Macizo Colombiano). The transect includes part of
Puracé Natural National Park, which extends from c. 2600-5000 m with the Serranía de Los
Coconucos and covers c. 830 km² between latitudes 1°50'-2°24'N and longitudes
76°07'-76°37'W in the departments Huila and Cauca. Diverse life zones are present in
this mountainous gradient; the high Andes and the páramo are biologically better known.

The regional geology presents a sequence: rocks from the Triassic-Jurassic, intrusive
Jurassic rocks, marine sedimentary rocks of the Cretaceous, Tertiary molasse deposits and
Quaternary deposits, which are related to orogenic volcanism or post-orogenic events in
the rise of the Central and the Eastern cordilleras (Kroonenberg and Diederix 1985). Among
the orogenic events, ignimbritic deposits characterize the landscape of the high plains,
which are associated with lava flows of small volcanoes such as Merenberg and El Pensil.
West of Puracé Volcano (4780 m) in the upper elevations of the massif is the Popayán
formation of lavas, ashes, conglomerates, tufa and fluvial deposits.

Along the altitudinal transect of these mountain systems are different types of soil,
as well as a wide variety of annual average temperatures and precipitation (Botero 1985;
Rangel-Ch. and Espejo-B. 1989). From 500-1100 m in the tropical or equatorial region, in
the alluvial plain of the Magdalena River and the foothills of Tesalia and Paicol, the
prevailing soils are haplustalfs; the annual average temperature is 30°C, the
precipitation varies between 1702-2108 mm. From 1150-2500 m in the higher tropical fringe
and the sub-Andean region on recent colluvium, dystropept and haplustalf soils prevail;
the temperature averages 18°C, the precipitation 1974 mm. From 2500-3300 m in the Andean
montane region, in landscapes of ignimbritic high plains of old colluvium and ash mantles,
dystropepts and dystrandepts prevail; the temperature is 15.2°C, the precipitation 1975
mm. From 3300-4400 m in the páramo region are moraines, deposits of pyroclasts, mud-flows
and colluvium, with troposaprists, tropofluvents, hydrandepts and dystrandepts prevailing;
the average temperature varies from 8°C to 5°C, the precipitation averages 2263 mm.

Although most often the rainiest month is May and the driest is January, and the mean
monthly temperature may be lowest in about July to August and highest in about February or
March, there is extreme diversity and even contrast from one part of the transect to
another. Data on the seasonal variations with altitude through the year are presented in
Rangel-Ch. and Espejo-B. (1989).

In the páramo different types of vegetation occur, principally bunchgrass fields
("pajonales") particularly on the slopes dominated by Calamagrostis
species, "frailejones" of Espeletia hartwegiana subsp. centroandina
(Asteraceae) on sites with well-watered soils, and peat bogs of Distichia muscoides.
In the mid-elevations, the high-Andean forests (with trees to 10 m high) are dominated by Weinmannia
and Miconia, whereas farther down slope are higher forests (over 25 m) of two
strata in which Quercus humboldtii (Fagaceae) prevails. In adjacent zones following
the gradient are forests of Lauraceae. In the tropical fringe prevail forests of deciduous
foliage with Guarea guidonia (Meliaceae) and Leguminosae, and in semi-arid sites
columnar cacti.

The syntaxonomic arrangement for part of the transect vegetation is as follows
(Duque-N. and Rangel-Ch. 1989; Rangel-Ch. and Lozano-C. 1989; Rangel-Ch. and Franco-R.
1985):

There are enclaves of páramo vegetation at low altitudes, in marshy or boggy sites
originating from the damming of streambeds by volcanic flows (Kroonenberg and Diederix
1985). A typical example is at 2380 m with the peat bog of La Candelaria, close to the
Merenberg Nature Reserve, where in a short stretch are different stages of the sequential
vegetation process - from marshy sites with a few water holes where Guzmania gracilior,
Blechnum columbiense and Oreobolus venezuelensis prevail, to frailejones
physiognomically and floristically similar to those of the páramo zone at 3400 m, with Espeletiahartwegiana and Hypericum lancioides. In the ecotone with forest vegetation,
Hedyosmum huilense and Lauraceae prevail, and thickets are established of Diplostephium
floribundum, Weinmannia sp. and Miconia floribunda (Rangel-Ch. and
Lozano-C. 1986).

4. Tropical region
In the nearby tropical region, especially along the eastern slopes facing the Magdalena
Valley, different types of vegetation are established, with prevalence at 1000 m of Guarea
guidonia and Perebea sp. Three other communities along the gradient are: (i) Spondias
mombin, Hirtella americana and Mouriri myrtilloides at 1000900 m in
moist locales of the dry valley of the Magdalena River; (ii) Pithecellobium dulce, Xylosma
velutinum and Croton argyrophyllus at 780 m; and (iii) Stenocereus (Lemaireocereus)
griseus and Randia aculeata at 530 m.

The eastern slope of the Puracé Volcano and the Magdalena Valley are better known and
these data refer mainly to them. The western slope facing the city Popayán is less known
and the environmental impact in the surrounding area has been greater. The estimate of
1200 species of seed plants and ferns in the transect between 1000-4450 m corresponds to
431 genera of 167 families. Table 62 presents data on the
dominant families and genera and those families' distributions in the four life zones of
the gradient (Rangel-Ch. 1991; Lozano-C. and Rangel-Ch. 1989).

In the high zones or páramo, bunches of Calamagrostis macrophylla and C.
effusa are used to roof huts and for fodder. Species used to spice meats include Hypochoeris
sessiliflora (Asteraceae) and Azorella spp. (Apiaceae). In the treeline open
woods, the woody species are used for fuelwood. In the mid-Andean montane region,
reforestation programmes use the native Quercus humboldtii, Billia columbiana
("cariseco"), Alnus acuminata ("aliso" - Betulaceae) and Beilschmiedia
cf. sulcata (Lauraceae). Living hedges are made with Sapium cuatrecasasii
("lechero" - Euphorbiaceae), Cedrela montana (Meliaceae), Guazuma
ulmifolia (Ulmaceae), Spondias mombin (Anacardiaceae) and Styrax
leptactinosus (Styracaceae).

In localities of La Argentina and Serranía de las Minas are archaeological remains of
houses and tombs of pre-Columbian settlements. The earliest known complex societies of the
northern Andean highlands are in the Alto Magdalena region, which was densely populated by
indigenous communities well before the arrival of the Spanish. The early cultures like
those of San Agustín and Saladoblanco are of great archaeological and historical value,
showing year-round settlements in the Upper Magdalena region for 2500 years (Drennan
1985a; Herrera, Drennan and Uribe 1989).

On the eastern slopes in the region of La Plata Valley, the inhabitants were Yalcones,
Moscopanes and Quinchinas. The western slopes were inhabited by Paeces, Guambianos,
Puracés, Coconucos and Popayanes. Most of these groups are extinct. A community of the
Paece now lives in the neighbourhood of Puracé Volcano and Guambianos dwell in localities
near Silvia (INDERENA 1984). Their homelands must be protected.

The páramo region close to Puracé Volcano is an important landscape resource. In the
mid-elevation Andean region, the oak groves and other vegetation with Quercus
humboldtii are the last remnants of the original vegetation; the associated fauna,
especially birds and small mammals, find food there. Reforestation programmes with native
species obtain necessary germplasm in these sites. The peat-bog zone of La Candelaria is a
biological heritage that must be protected and studied in detail. There are over 50 lakes
in the park. In localities of the transect several rivers flow - some originating on the
mountaintops of the central massif. Conservation of these watersheds is vital to the
surrounding municipalities. Several sites have thermal waters; their careful exploitation
could bring in resources for conservation.

Threatened fauna in the region include mountain tapir (Tapirus pinchaque),
rabbit deer (Pudu mephistophiles), spectacled bear (Tremarctos ornatus),
Andean condor (Vultur gryphus) and black-and-chestnut eagle (Oroaetus isidori).
Regional endemics include a bicolored antpitta (Grallaria rufocinerea romeroana).
The Central Andean páramo Endemic Bird Area (EBA B60) and Subtropical inter-Andean
Colombia EBA (B12) embrace the entire Central Andean cordillera from the páramo down to
the subtropical (mid-Andean) forest. Twenty-seven restricted-range bird species occur in
these two EBAs, 14 of which are entirely confined to the region. Due to increasing
disturbance of the specialized vegetation, 15 bird species are considered threatened. In
the drier low-lying zones of the adjacent Cauca and Magdalena valleys, this area overlaps
with the Dry inter-Andean valleys EBA (B13), where four restricted-range birds occur.

In the páramo region close to the Puracé Volcano, sulphur is extracted by mining.
Indigenous people make use of the bunchgrasses for extensive cattle-ranching, and on drier
slopes, cultivate potatoes and barley. In the mid-part of the transect in the Andean
montane region, a clay is utilized in arts and crafts. In this same region, coffee
plantations exist, sometimes combined with grazing of cattle. In forested areas there is
timbering; the forests of mid-elevations and those of the altitudinal ecotone between
dense and open vegetation could be managed silviculturally, so that wood for the local
populations would be a permanent resource. In the last few years an illegal crop (Papaver
somniferum, opium poppy) has become a problem. Tourism is another resource - to visit
the thermal spas of San Juan and Pilimbalá, the scenic páramo landscape and the areas of
pre-Columbian settlement.

All areas suffer pressure from one or more factors of human origin. In the páramo, the
mining causes access roads to be constructed without concern for biology or conservation,
uncontrolled release of gases and solid residues into the atmosphere and disposal of
untreated wastes into creeks and gullies. Although on the slopes that face Popayán there
are indications of use as long as 2500 years ago (Drennan 1985b), the present cultivation
of potatoes has transformed large areas.

Also responsible for modifying the landscape is disorderly construction of roads to the
Puracé crater, and extensive cattle-ranching - which entails periodic burning of
bunchgrass fields and frailejones. This produces soil erosion. The drying-out of páramo
marshes and peat bogs constitutes irreparable damage, since it is in the highlands that
the rivers originate. In the mid-part of the region, deforestation and excessive felling
of trees have produced extensive cleared sectors, where soil erosion is worrisome.

Cinturón Andino Biosphere Reserve (declared in 1979) encompasses 8550 km² from Nevado
del Huila Natural National Park (1580 km²) southward as far as Cueva de Los Guácharos
NNP (90 km²) (Olaya-Amaya c. 1984), thus including Puracé NNP (830 km²), which was
first protected in 1961 and established in 1968 - it should be extended to protect
Paletará Valley (in Cauca), where areas of great biodiversity exist. A Forest Reserve
should be strongly supported to supply seeds and seedlings necessary for reforestation of
sites particularly in the mid-zone. The private Merenberg Nature Reserve (c. 3 km²),
which began in 1932, conserves remnants of oak forest from 2300-2800 m; while protecting
the reserve, in 1975 Mrs Mechthild Buch was murdered. Near the oak groves at 2300-2400 m,
a buffer zone should be created to include peat bogs with enclaves of páramo vegetation
and a representative portion of the zonal forest.In the vicinity of the Serranía de las
Minas localities with very humid atmosphere exist, due to orographic precipitation; oak
groves occur together with species of Alfaroa and Clusia in a unique
situation (Rangel-Ch. and Lozano-C. 1989).